As noted in the above-referenced prior application, existing arrangements which permit angular offsetting of crane boom extensions or jibs are varied and not entirely satisfactory from the standpoint of convenience of use, simplicity of construction and safety. Accordingly, the main objective of this invention is to improve on all known devices which enable angular offsetting of boom jibs particularly in these areas of convenience of installation and operation, simplicity of construction and safety of the operator or installer of the means which supports the jib in its several offset positions.
More particularly, it is an object of the invention to provide an offsettable extension or jib for crane booms which is held in each of its several offset positions by a single fixed length self-adjusting cable loop or guy. The loop or guy has its ends attached to the nose assembly of the boom and extends around a fixed arcuate guide mounted on an inclined plane bracket which is attached to the jib relatively close to its outer end, the inclination of the mounting bracket relative to the axis of the jib defining the plane occupied by the cable loop in all adjusted positions of the jib and also establishing a constant angle between the cable loop and the jib axis in all offset positions of the jib.
A major feature of the device is the ability of the jib to assume its several different angular positions relative to the boom axis merely by repositioning the cable loop guide and fixing it in a corresponding number of positions on the inclined plane bracket.
The device is safer than prior art devices for the same general purpose inasmuch as the use and installation of separable jib support links and guy cables is eliminated. These prior art components have generally required the installer or operator to climb onto the crane boom while it is in a depressed position to install links or cables associated with the jib. The present device does not require this because of the fact that the inclined plane bracket on which the multiple position cable loop guide is held is located near the forward end of the jib and consequently is very close to ground level when the crane boom is in its maximum depressed position. Therefore, an installer standing on the ground can place the cable loop around the arcuate guide and can also adjust the position of the guide on the inclined plane guide mounting bracket with complete safety.
Other features and advantages of the invention will become apparent during the course of the following detailed description.